Multilayer optical data storage device

ABSTRACT

A multilayer optical data storage device is disclosed which has at least two spaced apart storage layers, each of such layers being adapted to store information; a spacer layer positioned between alternating storage layers; and at least one of the layers including tracking and/or format information, and at least one storage layer that does not include substantial tracking and/or format information.

CROSS REFERENCE TO RELATED APPLICATION

Reference is made to commonly assigned U.S. application Ser. No.08/715,267 filed concurrently herewith, entitled "Writing ApparatusUsing a Multilayer Optical Data Storage Device" by Edward C. Gage et al,and commonly assigned U.S. application Ser. No. 08/611,266 filed Mar. 5,1996, entitled "Optical Storage Device Including Multiple RecordingLayers" by Randall H. Victora et al, the teachings of which areincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to optical data storage devices which haveat least two spaced apart information recording layers.

BACKGROUND OF THE INVENTION

Multilayer optical recording devices are known and offer enhancedrecording density. Essentially, these devices consist of two or morerecording surfaces spaced sufficiently far apart that each surface canbe read and recorded independently.

The provision of tracking and formatting information for each layer hasreceived attention in the literature. See, for example, K. A. Rubin, H.I. Rosen, W. W. Wang, W. Imaino, and T. C. Strand in SPIE Vol. 2338, p.247, 1994 who suggest the use of polycarbonate substrates with thegrooves for tracking stamped into them. The two recording layers areseparated at a fixed distance with the spacer layer consisting mostly ofair. In this arrangement, there are two substrates and they form theexterior of this sandwich structure. Problems with this arrangementinclude the difficulty in aligning the substrates during manufacture,and the limitation of only two layers.

The Digital Video Disk employs unusually thin 0.6 mm polycarbonatesubstrates. One arrangement proposed for use in this system providesadditional rigidity: instead of an air gap the two recording layers areglued together with an optically transparent adhesive.

An entirely different approach is described in "Plain Talk: Dual-LayerCompact Disc" 3M CD-ROM Services, St. Paul, Minn. (1995). This approachuses a polycarbonate substrate with grooves stamped into it forproviding tracking information for one layer and an UV-curablephotopolymer layer deposited atop the first recording layer and thenstamped with the necessary information for the second layer. Thisprocess is relatively slow and suffers from difficulty in aligning thesubstrate with the stamper for the photopolymer layer.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide either tracking orformat information on at least one layer of a multilayer recordingdevice in a cost-effective way.

This object is achieved in a multilayer optical data storage device,comprising:

(a) at least two spaced apart storage layers, each of such layers beingadapted to store information;

(b) a spacer layer positioned between alternating storage layers;

(c) at least one of the layers including tracking and/or formattinginformation, while another layer does not include substantial trackingand/or formatting information; and

(d) each layer containing information identifying that layer.

These and other aspects, objects, features and advantages of the presentinvention will be more clearly understood and appreciated from a reviewof the following detailed description of the preferred embodiments andappended claims, and by reference to the accompanying drawings.

ADVANTAGEOUS EFFECT OF THE INVENTION

Advantages of this invention are that disks made in accordance with thepresent invention will have a favorable capacity/cost ratio.

Optical storage devices in accordance with the present invention workswith MO, WORM, and erasable phase change disks that are formatted planaror pregroove devices.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a two-sided multilayer recording optical storage device inaccordance with the present invention;

FIG. 2 shows a single-sided multilayer recording optical storage devicein accordance with this invention;

FIG. 3 shows in schematic form more details of a representative of anoptical drive apparatus for using the devices of FIGS. 1 and 2;

FIGS. 4, 4A and 4B show a flow chart of the operation of the opticaldrive apparatus of FIG. 3; and

FIG. 5 is an expanded diagram of block 70 shown in FIG. 4.

DETAILED DESCRIPTION OF THE INVENTION

By use of the term "tracking information" is meant that information usedfor determining the location of the radial position on a device. Forexample, grooves or marks on a disk can be used to provide suchinformation. By use of the term "format information" is meantinformation contained on the device, that is used by the optical driveapparatus such as for example, header information, sector information,and timing information that are usually provided by marks or a wobble ina tracking groove. Further format information may include diskidentification and disk characteristics, such as optimum record powerand optimum read power.

By use of the term "substantial tracking information" is meantinformation for determining the location of at least 20% of the tracksto be recorded on a particular layer. By use of the term "substantialformat information" is meant at least 20% of the bytes of formatinformation to be recorded on a particular layer.

As shown in FIG. 1 there is provided a multilayer two-sided opticalstorage device 9 having a substrate 10 which can be made of anyconvenient material such as aluminum. The device 9 can be in the form ofa disk. A recording layer 12 is formed over the substrate 10.Intermediate planarizing sublayers 13 can be formed between therecording layer 12 and the substrate 10. Typically, the recording layercan be made of phase change material, rare earth transition metalalloys, cobalt/platinum superlattices, or dyes. As shown, there are aplurality of spaced apart recording layers 12 each separated by its ownspacer layer 14. The recording layer 12a will be understood to includetracking and format information while the other recording layers 12 donot as manufactured. Typically the spacer layer 14 can be air, atransparent organic material, or the like. A protective layer 16 ispositioned over the top of the top recording layer 12. Each of therecording layers 12 may contain layers additional to an active layer,such as dielectric layers or reflective layers used for opticalenhancement or protection. As will be described subsequently, an opticalhead is used to write and read data from the recording layers. The head,of course, is part an actuated device and includes a light source 18which focuses light on the different layers 12 for recording. Since theoptical storage device 9 is two-sided, the recording layers 12 on eachside are independent although they can be used simultaneously.

Turning now to FIG. 2 where another, but single-sided, multilayeroptical storage device 9 in accordance with the invention is shown.Where parts in FIG. 2 correspond to those in FIG. 1 the same numberswill be used. FIG. 2 is similar to FIG. 1 except that the substrate 10is made of a transparent material such as glass or polycarbonate andthat no protective layer 16 is used. The substrate 10 in this embodimentprovides the same function as the protective layer 16. In the FIG. 1arrangement light, of course, passes through the top protective layer 16and illuminates the recording layers 12. In the FIG. 2 arrangement,light passes through the transparent substrate 10. Of course, atwo-sided disk could be constructed by laminating two devices 9.

The recording layers 12 are mechanically separated by the spacer layer14 that would be on the order of 10 to 100 μm thick. Thus only onerecording layer 12 is in focus for a given beam. The format or trackinginformation can be mechanically contained in the substrate, grooveddisk, or soft formatted using a servo writer. Typically, master layersemploying mechanically recorded information such as grooves would beadjacent to the substrate 10, while the servo written master layer couldbe any recording layer 12. An important factor is that one of therecording layers will include tracking and/or format information (layer12a) while another one does not. In both FIGS. 1 and 2 there is a seriesof these recording layers with spacer layers and it is a matter ofdesign selection as to which recording layer will have tracking and/orformat information.

A preferred embodiment of this invention is to limit the prerecordedinformation on the layers 12 (other than layer 12a). An importantexception to this principal is layer identification that permit theoptical drive apparatus to determine which layer is being accessed.According to the invention, there will be at least one layeridentification label per layer in the disk as manufactured. This labelmight, for example, be a binary representation of a number or anarrangement of bits yielding a particular frequency when read from arotating disk in form of a few tracks. A possible implementation of thisinvention is to replicate this layer identification label in subsequentformat information written on layers 12 by the optical drive apparatus.

Turning now to FIG. 3, where an optical drive apparatus 20 in accordancewith the present invention is shown. The apparatus 20 includes twoseparate optical heads 21a and 21b which respectively include their ownactuators. Each actuator 22a and 22b is conventional in construction andincludes an objective lens 24. By using two separate actuators 22a and22b mechanically and electronically linked, tracking and sectorinformation are obtained from the appropriate recording layer of theoptical storage device which was preformed or formatted.

In FIG. 3, the two optical heads 21a and 21b are mounted on a radialaccess carriage 23 positioned over the optical recording device 9 shownin FIGS. 1 or 2. The carriage 23 translates in a radial direction boththe optical heads 21a and 21b relative to the top surface of the opticalrecording device 9. Optical head 21a is conventional and has bothtracking and focusing capabilities. Optical head 21a providesconventional tracking error (TES) and position sensing signals (LPS).The tracking error signal provided by optical head 21a is provided to ananalog to digital converter 25 which digitizes the tracking error signaland provides a digital input signal to drive processing circuit 28. In asimilar fashion the optical head 21a produces a lens position signal(LPS) which is digitized by an analog to digital converter 26 and thisdigital signal is applied to the drive processor circuit 28. The opticalhead 21a is a low cost read head that has focus and tracking sensors.The optical head 21b can also be conventional and provides trackingerror (TES) and lens position signals (LPS) which are respectivelydigitized by A/D converter 30 and 32 respectively. These digital signalsare also applied to the drive processor circuit 28.

For purposes of illustration we assume that a single-sided opticalstorage device 9 (See FIG. 2) includes four write-once recording layerswhere the layer 12a nearest the substrate is preformatted with trackinginformation and sector header information (format information). Thedrive processor 28 outputs signals to control the tracking actuator ofthe read and read/write head 21a and 21b through D/A converters 33a and33b and power amplifiers 34a and 34b respectively.

Table 1 shows the role of the two optical heads 21a and 21b when readingand writing data from the various layers of the FIG. 2 device 9. Opticalhead 21a is continuously focused on the recording layer that containstracking and format information. Initially the device 9 will only havesubstantial tracking information on one recording layer 12 which islabeled 12a. While this recording layer 12a is being read or written on,a tracking look-up table may be constructed by the drive processorcircuit 28 using the tracking signals and lens positions from both ofthe optical heads 21a and 21b. The actuator drive signal produced by thedrive processor circuit 28 are used to control the position of theactuators 22a and 22b. When writing any other layer, the trackingactuator drive current for 22b will be derived from the tracking errorsignal and lens position from optical head 21a and the tracking look-uptable previously constructed. When reading from a recording layer 12a,optical heads 21a and 21b will produce tracking error signals and lensposition signals that are used by the microprocessor 24 for changing thetracking look-up table. The look-up table thus constructed is stored inmemory included in the drive processor circuit 28.

                                      TABLE 1                                     __________________________________________________________________________    Example for Four Layer Media with two actuators                                                       Tracking                                                                      Actuation                                                                            Tracking Look-up                               Function                                                                           Layer                                                                            Optical Head 21b                                                                      Optical Head 21a                                                                      Signal Table Status                                   __________________________________________________________________________    Read 12a                                                                              F,T,R, @L12a                                                                          F,T,R @L12a                                                                           #2lb @L12a                                                                           Updating                                       Write                                                                              12a                                                                              F,T,R,W @L12a                                                                         F,T,R @L12a                                                                           #2lb @L12a                                                                           Updating                                       Read 12 F,T,R @L12                                                                            F,T,R @L12a                                                                           #2lb @L12                                                                            Updating                                       Write                                                                              12 F,R,W @L12                                                                            F,T,R @L12a                                                                           #21a   Locked in Use                                                          @L12a + Table                                         __________________________________________________________________________     F = focus, T = tracking, R = read, W = write, L = recording layer        

The first and second columns of Table 1, respectively, indicate thecommanded read/write function on any of the layers. Column 3 shows thefunctions being performed by the read/write optical head 21b, on theappropriate layer (@L) and column 4 shows the function of the opticalhead 21a focused on layer 12a. The tracking actuator signal (TES) sourcefor the read/write head is shown in column 5. During read, the opticalheads 21a and 21b always use their own TES signal for the tracking errorservo, but during writing of a non-formatted layer, the read/writeoptical head 21b uses the information from optical head 21a tracking onlayer 12a plus the tracking look-up table. The status of the trackinglook-up table is shown in column 6.

The tracking look-up table may contain more than a simple offset of lensposition signals (LPS). It may contain offset and gain as a function ofdisk rotation angle, layer number, radius, and frequency. It may alsocontain information about the differences in the two actuators, angularoffset, gain, frequency response, etc. The information in the trackinglook-up table may be calculated from the lens position signal andtracking error signal from the two heads. When a device 9 is inserted,the apparatus may recall the table from memory, go to reading the masterlayer to obtain disk information and build the tracking look-up table,or it may wait for a request to write to a recording layer. When writingto recording layers 12 other than the recording layer 12a, sectorheaders and tracking information can also be written.

Turning now to FIG. 4, which is a flow chart of a method of operation ofthe optical drive apparatus 20. For purposes of illustration, we willdiscuss one application of the invention with write-once media. After aread or write command 40 is received the optical drive apparatus 20responds as follows: the carriage 23 seeks to the disk directory 42 onthe device 9. The read head 21a acquires focus on layer 12a. This isshown in block 44a. Next, the read head 21a acquires track (See block46a). As this process proceeds, the read head 21a reads the directoryinformation and stores in memory the desired recording layer and thememory address to be used for the read or write command (See block 48a).

The read/write head 21b acquires focus on the layer 12 (See block 44b),at the same time the read/write head also acquires track (See block46b). The read/write head 21b reads the layer identification labels (Seeblock 48b) to verify layer identity. In block 50, during the readprocess the lens position signals from the read and read/write opticalheads LPS signals are differenced and stored in memory to construct thetracking look-up table as shown by the equation in block 50. Thecarriage 23 is now moved so that the read/write head 21b is positionedat the correct location to access the desired address radius on adesired recording layer 12 (See block 52). At this point the driveprocessing circuit makes a decision. If reading is to be accomplishedthen the read/write head 21b, using its tracking error signal, acquirestrack as shown in block 46b. The reading process then continues inconventional fashion as depicted in block 58.

If the apparatus 20 has to write then the appropriate recording layer 12is found. If that layer is layer 12a, the read/write head acquires track(See block 46b) from its tracking error signal. A verification processis now accomplished where the read/write head determines that there areblank areas to be written (See block 62). If the verification ispositive then the read/write head will write data (See block 64). If alayer other than 12a is to be written to then the read head acquirestrack in a convention manner (See block 46a). If the layer 12 is blankthen the read/write head moves directly to block 70 and acquirestracking information from the lens position signal from each opticalhead 21a and 21brespectively and a previously constructed look-up table.During write the LPS from each head are differenced and the look-uptable is subtracted. This quantity is servoed to a zero value andLPS_(read) (φ)-LPS_(read/write) (φ)-L(φ)=0, so that the actuators havethe same lens offsets at each angle as they did at the last look-uptable construction. The variable φ means angular position of the opticalstorage device. This arrangement will be described in more detail inreference to FIG. 5. However if the layer 12 has been partially written,then the following sequence takes place: Carriage 23 will be moved tothe last written position as shown by block 72. Then the read/write headacquires track as shown in block 46b. Finally, a blank check 62 is runas previously described. In block 74 during the blank check, thetracking look-up table will be updated to contain the lens positionsignal difference from the read head and read/write head as the lastpreviously written position of the optical device 9 is read.

Turning now to FIG. 5 wherein an expanded diagram of block 70 will bedescribed. The look-up tables constructed as in blocks 74 or 50 will beunderstood to be included in tracking look-up table 80. The constructionof FIG. 5 shows the servo control of the read optical head 21a and theservo control of the read/write optical head 21b. The read optical headtracking error servo will first be described. The optical head 21a, asis conventional, produces TES and lens LPS. These signals are providedto analog digital converters 25 and 26 respectively as shown in FIG. 3.The sampled TES signal is used by the drive processing circuit 28 toproduce an actuator drive signal by using predetermined tracking errorgain circuit 82, tracking offset 84, and compensation circuit 86. As isquite conventional, D/A converter 33a provides an input to a poweramplifier 34a which produces the actuator drive signal for the opticalhead 21a. The analog to digital converter 26 provides a sampleddigitized lens position signal to a timed-delay circuit 100. Thetimed-delay circuit provides input to a subtractor 102 within theprocessing circuit which subtracts from the lens position the lensposition signal from the optical head 21b. The time delay processsynchronizes the LPS as a function of φ since the optical heads may havedifferent angular offsets depending on their carriage mounting. Theoptical head 21b drives the A/D converter 32 as has previously beendescribed. The previously construction look-up table 80 is thensubtracted from the differenced lens position signals and an input isprovided into a tracking error gain circuit 104. Next this signal isprovided to a compensation circuit 106 which drives a D/A converter 33bwhich drives the power amplifier 34b as previously described. Thus, thetracking motion of the read/write head's actuator is servo controlled tomaintain the LPS difference stored in the tracking look-up table (80)and quality writing is maintained; i.e. constant track pitch.

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention. For example, the description of FIG. 4 describes oneexample of a sequence particularly appropriate to WORM media, but thepresent invention will be understood to be usable with other types ofmedia. Also, the technique, described in this application, of copyingtracking and format information from one layer to another could be donewithout writing user data, possible as part of the finishing operationat the factory.

PARTS LIST

9--multilayer optical storage device

10--substrate

12--recording layer

12a--recording layer

13--intermediate planarizing sublayers

14--spacer layer

16--protective layer

18--light source

20--optical drive apparatus

21a--optical head

21b--optical head

22a--actuator

22b--actuator

23--radial access carriage

24--objective lens

25--A/D converter

26--A/D converter

28--drive processing circuit

30--A/D converter

32--A/D converter

33a--D/A converter

33b--D/A converter

34a--power amplifiers

34b--power amplifiers

40--read or write command

42--carriage seeks to disk directory

44a--acquire focus

44b--acquire focus

46a--acquire track

46b--acquire track

48a--read

48b--read

50--construct tracking look-up table

52--move carriage

58--read data

62--blank check

64--write data

70--read/write head servoed

72--move carriage

74--construct look-up table

80--look-up table

82--tracking error gain circuit

84--tracking offset

86--compensation circuit

100--time delay circuit

102--subtractor

104--tracking error gain circuit

106--compensation circuit

We claim:
 1. A multilayer optical data storage device, comprising:(a) atleast two spaced apart storage layers, each of such layers being adaptedto store information; (b) a spacer layer positioned between alternatingstorage layers; (c) at least one of the layers including trackinginformation, and at least one storage layer that does not includesubstantial tracking information; and (d) each layer containinginformation identifying that layer.
 2. The optical storage device ofclaim 1 where one of the layers is a recording layer which has preformedinformation.
 3. The optical storage device of claim 1 where at least oneof the layers is a recording layer which records information by means ofa focused light beam.
 4. The storage device of claim 1 where at leastone of the layers that does not include substantial tracking informationcontains some tracking information.
 5. A multilayer optical data storagedevice, comprising:(a) at least two spaced apart storage layers, each ofsuch layers being adapted to store information; (b) a spacer layerpositioned between alternating storage layers; (c) at least one of thelayers including format information, and at least one storage layer thatdoes not include substantial format information; and (d) each layercontaining information identifying that layer.
 6. The optical storagedevice of claim 5 where one of the layers is a recording layer which haspreformed information.
 7. The optical storage device of claim 5 where atleast one of the layers is a recording layer which records informationby means of a focused light beam.